This invention relates to an automatic masking device for an original picture holder used in a composer for printing repeatedly original pictures onto a photosensitive material such as a film, a plate, or the like.
An original picture to be held on an original picture holder is usually smaller than the entire effective surface of the original picture holder, and accordingly the part of the original picture holder surrounding the original picture is usually masked off.
FIGS. 1(a), 1(b), 2 and 3 of the drawings show the general layout of a prior art original picture holder. The original picture, which comprises a pattern 2 and register marks 3 around it, is shown in FIG. 1a. This is attached to an original picture holder, and is contact-printed onto a photosensitive material, a cut mask 4 having transparent portions in it being laid on the original picture 1 so as to mask off its periphery. The transparent portions correspond to the pattern 2 and the register marks 3. This cut mask 4 is shown in FIG. 1b.
The manner of doing this is as follows. The original picture 1, as shown in FIGS. 2 and 3, is positioned and attached in a central position on one side of a transparent mounting sheet 5 so that its base surface contacts therewith. The cut mask 4 is attached onto the opposite surface of the transparent mount sheet 5, in a position corresponding to that of the original picture 1, and the assembly thus formed is held onto the contact surface 6a of a transparent plate 6 by a vacuum suction means or the like.
Then, this original picture holder is positioned on the photosensitive material so as to contact the original picture 1 with the photosensitive material, and the pattern of the original picture is printed by light directed onto it through the transparent plate 6 onto the photosensitive material.
In FIGS. 2 and 3, the numeral 7 denotes masking means for masking off an unnecessary register mark 3 when the pattern 2 is printed, which is arranged on the opposite surface of the transparent plate 6 from the contact surface 6a, and is slidably moved.
As the automation of the other parts of the composer has become more and more advanced, along with the surrounding devices which are used with the composer, and automatic exchange of original pictures and printing plates has become possible, a fully automatic composer which might operate for a long time without operator attention has been envisaged. For this, automatic masking would be necessary.
Recently an automatic masking device has been developed, in which the pattern size and so forth of the original picture to be photo-composed are written on a control tape of a NC control machine, a computer, or the like, which automatically controls the actions of the composer for a long time, and the effective exposure surface of the original picture holder is varied by the control tape. However, this form of automatic masking is time-consuming, costly, and unsatisfactory: the information for driving the automatic masking device must be written on the control tape, etc., beforehand. Therefore, a simpler form of automatic masking has been desired.